Replace command-line scripts with console scripts

[nfahlgren]

Describe your changes
The currently included plantcv-workflow.py, plantcv-utils.py, and plantcv-train.py scripts do not work well on Windows systems. Additionally, the minimal code in these scripts are not tested (the important underlying code is already).

This PR replaces these scripts with cli modules that are used to build installable programs (console scripts) at the time of installation. After installation the programs are now named: plantcv-run-workflow, plantcv-train, and plantcv-utils.

Type of update
Is this a: New feature or feature enhancement

Associated issues
Supersedes #617
Closes #616

For the reviewer
See this page for instructions on how to review the pull request.

• PR functionality reviewed in a Jupyter Notebook
• All tests pass
• Test coverage remains 100%
• Documentation tested
• New documentation pages added to plantcv/mkdocs.yml
• Changes to function input/output signatures added to updating.md
• Code reviewed
• PR approved

[codecov]

Codecov Report

Merging #1099 (5cb6cd4) into release-4.0 (89cfe7b) will not change coverage.
The diff coverage is n/a.

@@              Coverage Diff               @@
##           release-4.0     #1099    +/-   ##
==============================================
  Coverage       100.00%   100.00%            
==============================================
  Files              161       164     +3     
  Lines             6875      7004   +129     
==============================================
+ Hits              6875      7004   +129     

Flag	Coverage Δ
unittests	100.00% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
plantcv/learn/cli.py	100.00% <ø> (ø)
plantcv/parallel/cli.py	100.00% <ø> (ø)
plantcv/utils/cli.py	100.00% <ø> (ø)